This application is directed to sunlight responsive thermochromic window systems and, more particularly, to window structures for thermochromic window systems.
A conventional window for the residential market consists of a double pane unit with a clear piece of glass on the outside and a low-E piece of glass on the inside pane with the low-E coating face outwards. A conventional high performance window for commercial applications utilizes a double pane construction with a tinted glass pane on the outside and a low-E coating either on the tinted glass or on the second pane of glass.
Sunlight responsive thermochromic (SRT) windows are variable tint windows that darken and lighten based on the amount of sunlight shining directly on the window. Exemplary examples of thermochromic windows include U.S. Pat. Nos. 6,446,402 and 6,084,702 to Byker et al., the contents of which are incorporated herein by reference.
Windows provide a significant design challenge for architects and builders. Large, high transmission windows are desirable for providing an open-air feeling to building occupants, providing significant solar heat gain when sunlight is directly on them and for allowing visible light into a building to provide daylighting and thereby substantially reduce the need for electric lighting during the time when occupants are most often present. However, conventional windows are problematic for admitting excessive amounts of solar heat when air conditioning is already in use. This is especially true at certain times of the day and certain parts of a building when the solar radiation is shining directly on or through the windows.
An attempted solution to the problem is the use of window treatments like shades, drapes and blinds. However these are expensive, cumbersome and aesthetically undesirable solutions, particularly in large office buildings, hotel atria and airport terminals. With control of sunlight by thermochromic windows, the need for conventional blinds and shades, to control heat gain and glare, is minimized, this also enhances energy savings in that artificial lighting needs will be reduced. Large window designs become acceptable when the challenge of excessive heat load can be met with the straightforward window dimming capability provided by thermochromics.
Insulated glass (IG) is referred to throughout this disclosure with the meaning of insulated glass or plastic, as interchangeable elements. IG construction assures sufficient insulation performance regardless of outside ambient temperatures or convective heat loss due to air movement over the outboard window pane.
As an absorbing window pane is heated by the sun, even in the absence of wind, thermal currents are induced and natural convection occurs. SRT window designs must account for these thermal currents as well as wind-induced thermal effects to maintain superior window performance during daylight service. Architects and building designers desire window energy savings performance, excellent sound reduction along with the capability of using a self-cleaning layer, safety performance, resistance to fire, blast, bullets and hurricanes. Glazing installers desire the ability to fit windows with traditional methods without wires, power supplies, energy management systems and controllers. SRT windows can provide substantial energy savings compared to traditional window systems.
Accordingly, there is a need for a thermochromic window system to trap the sunlight energy, and keep it from penetrating inside the building. Furthermore, the trapped heat energy may be redirected to either the inside or outside of the building by the thermochromic window system while diminishing glare from the sun.